The Resolution Integral as a metric of performance for diagnostic grey-scale imaging

There is a strong clinical need for objective measurements of grey-scale ultrasound imaging performance. We have previously proposed the Resolution Integral R as a suitable metric, because it defines the ratio of the penetration of an ultrasound beam in soft tissue to the ultrasound beam width. Transducers with good performance combine deep penetration with high lateral resolution, giving a large ratio of penetration to beam-width. Depth of Field LR and Characteristic Resolution DR are defined such that R = LR/DR. LR defines a region of optimum resolution, and DR is representative of the lateral and elevation resolution within LR. We report the results of a survey of the imaging performance of 79 models of ultrasound scanner made using an Edinburgh Pipe Phantom to measure values of R, LR and DR. The scanners were manufactured between 1986 and 2009 and were from 23 manufacturers. A total of 171 different transducers were tested, including linear and convex arrays, and mechanical sector probes. The results demonstrate that R successfully distinguishes transducers with differing levels of performance, and that LR and DR characterise probes suitable for different clinical applications. The characteristics of individual probes are concisely quantified and displayed on a plot of LR vs DR.